With this morning's launch of the space shuttle Endeavour , the six-astronaut crew began what NASA is calling a "very complicated" mission to deliver and install the last major piece of the International Space Station.

After cloudy skies stymied Sunday's scheduled launch, Endeavour finally took off at 4:14 a.m. EST today from NASA's Kennedy Space Center in Florida. Just two minutes into the flight, the space shuttle entered low-Earth orbit and began its trip to rendezvous with the space station on Wednesday.

"What a beautiful launch we had this morning. The orbiter performed extremely well," said Bill Gerstenmaier, associate administrator for Space Operations, during a postlaunch news conference. "This is a great start to a very complicated mission."

The weather was a concern in the hours leading up to this morning's launch. NASA had called for a "no-go" a few times between Sunday night and Monday morning but the low-cloud cover lifted in time for the smooth liftoff.

The space shuttle originally was scheduled for a Sunday morning liftoff but a low cloud ceiling forced NASA to cancel with the astronauts suited up and strapped into their seats.

The second try was a smooth one, said Mike Leinbach, shuttle launch director. "This was one of the smoothest countdowns ever," said Leinbach. "The team was very, very energized going into the count."

The six Endeavour crew members are set to head to the orbiting space station to deliver an Italian-built module that will be connected to the station, along with a seven-windowed cupola, which will serve as a robotics control room.

The astronauts are set to conduct three spacewalks during the mission.